The two men, whose identities are being withheld, had been on antiretroviral (ARV) drug therapy for years before being diagnosed with lymphoma, a cancer of the lymph nodes.

Both underwent intensive chemotherapy followed by bone marrow transplants to treat the cancer. They remained on antiretroviral therapy.

Approximately four months after the transplant doctors were still able to detect HIV in their blood, but six to nine months later, all traces of the virus were gone.

"Because of those findings, we thought it was justified to take the patients off of their therapy to see what happens," said Dr. Timothy Henrich, who conducted the clinical trial.

"Now, in a normal person who has HIV, who has been on long-term antiretroviral therapy for years, usually the virus comes back within two to four weeks after stopping therapy, it comes right back. "

Some patients make it up to eight weeks before the virus returns, said Henrich, a researcher at Harvard Medical School and Brigham and Women's Hospital in Boston, but the virus returns eight to 10 weeks after therapy is stopped in the vast majority of patients.

Not so for these two, however.

"We are now recording 15 weeks after therapy and eight weeks after therapy for our two patients, and to date we are unable to detect HIV rebounding in the bloodstream after we stopped the therapy," Henrich said.

"We do weekly monitoring, as well. We've been looking at the virus in the blood and the cells in the blood essentially every week since we've taken them off therapy, and we have not been able to detect virus at this time."

The two men are being compared to Timothy Ray Brown, also known as the "Berlin Patient." Brown is thought to be the first person ever "cured" of HIV/AIDS.